The invention concerns a novel niobium wire, a process for producing it, and its use for connection to niobium or niobium oxide capacitors.
Wires made of refractory metals are used for the electrical connection of metal powder capacitors. Tantalum wires are generally used for this purpose. This has the disadvantage of a relatively high sintering temperature. As a result, the surface of the powder anode cannot be completely used, because the powder partially sinters together. Furthermore, the use of tantalum wires with niobium and niobium oxide capacitors results in non-recyclable waste. Moreover, the price of tantalum is subject to considerable speculation, so that the costs for the raw material are difficult to calculate and control.
Niobium wires have already been recommended for the connection of powder anodes. For example, U.S. Pat. No. 6,358,625 B1 describes anode wires made of niobium or tantalum, which, to improve adhesion, are treated with oxygen in such a way that surface enrichment on the order of 35 atom % in a thickness of about 50 nm is obtained. Niobium and tantalum wires normally contain only small amounts of oxygen. Oxygen concentrations of 50-300 μg/g are specified for tantalum. The surface enrichment does not affect the general properties, such as conductivity, but increases adhesion. Sintering temperatures around 1,250° C. are specified.